Heat treating furnace



Nov. 24, 1936. w. E. KINGSTON 2,

" HEAT TREATING FURNACE I Filed Aug. 7, 1935 E Lip O 5 1 Q ru *==lINVENTOR ATTORNEY immefhrvesnw.

Patented Nov. 24, 1936 UNITED STATES PATENT OFFICE HEAT TREATING FURNACEApplication August 7, 1935, Serial No. 3541?;

6 Claims.

This invention relates to heat treating furnaces and particularly,although not necessarily limited thereto, to a furnace for heat treatingthe metal parts of electric lamps, radio tubes and similar devices.

A principal object of the invention is to provide an improved furnace inwhich the parts to be heat treated, may be subjected to a relativelyhigh temperature in the presence of a non-oxidizing atmosphere.

Another object is to provide a furnace in which metal parts may be heattreated in an atmosphere of hydrogen or other similar reducing gas.

Another object is to provide a conveyor type furnace for heat treatingparts in an atmosphere of a gas which is highly explosive when mixedwith air, the furnace being designed to prevent such an explosivemixture.

A feature of the invention relates to a furnace for heat treatingobjects in the presence of a reducing gas such as hydrogen, the furnacebeing so designed that the specific gravity of the hydrogen is utilizedto prevent the formation of an explosive mixture within the furnace.

Another feature of the invention relates to a continuous heat treatingfurnace employing an atmosphere of hydrogen or other similar explosivegas, the furnace being designed so that the charging and dischargingends are unsealed, but without the danger of the gas forming anexplosive mixture within the furnace.

A still further feature relates to a heat treating furnace of theconveyor type employing an atmosphere of hydrogen the furnace beingprovided with a main heat treating chamber and ingress and egress ductsso proportioned and arranged with respect to the main chamber that thehydrogen seals itself within the chamber and insuificient air isadmitted to the higher temperature parts of the furnace to form anexplosive mixture.

A still further feature relates to the novel organization, arrangementand relative location of parts which go to make up a safe and eflicientheat treating furnace employing an atmosphere of hydrogen or similar gasor mixture of gases.

Other features and advantages not specifically enumerated will beapparent after a consideration of the following detailed descriptionsand the appended claims.

In the drawing which represents one preferred embodiment of theinvention,

Fig. l is a front elevational view of the furnace embodying features ofthe invention.

Fig. 2 is a top plan view of the furnace shown in Fig. 1.

In certain of the arts, particularly in the electric lamp and radio tubearts, it is necessary to employ metal parts which are free as much as 5possible from surface contamination as well as from occluded gases inthe body thereof. Accordingly it is the usual practice to subject suchparts to a heat treatment whereby they are raised to a. sufficientlyhigh temperature to drive out the 10 entrapped or occluded gases. Inorder that this heat treatment may not oxidize or otherwise destroy thesurface of the metal parts it has been customary to effect the heattreatment in the presence of a non-oxidizing atmosphere. It has 5 alsobeen found desirable to effect this heat treatment in the presence of areducing atmosphere such as hydrogen but one of the difficulties ofusing hydrogen is the danger of its forming an explosive mixture withair at high temperatures. For this reason it has not been foundpracticable to build a continuous or conveyor type heat treating furnacewith a hydrogen atmosphere in the furnace. I have found that byspecially designing the arrangement and proportions of the 25 furnaceparts it is possible to take advantage of the very great lightness ofthe hydrogen so that the formation of an explosive mixture within thefurnace is avoided. In carrying out this phase of the invention thefurnace is provided with a main heat treating chamber which is filledwith an atmosphere of hydrogen, and ingress and egress ducts areprovided for the main chamber of such length and inclination withrespect to the main chamber that the hydrogen which is sup- 35 plied tothe main chamber in the manner set forth, remains effectively sealedwithin the furnace even though the ingress and egress open ings for thefurnace are not air sealed. Consequently it is practicable to carry theparts to 40 be heat treated through the furnace on a continuous conveyorthe speed of which may be accurately regulated. As a result, the partssuch for example as the metal parts of a lamp or tube, are given auniform and efficient heat treatment 5 Referring to the drawing thefurnace comprises in general a main heating chamber l preferably of arefractory metal and preferably although not necessarily, rectangular incross section. The main chamber is united to inclined duct portionsdesignated generally by the numerals 2 and 3, respectively, the duct 2arranged to act as the ingress duct for the conveyor belt 4, while theduct 3 is the egress duct, it being understood of course that the ductsare hermetlcally joined to the opposite ends of the main chamber bysuitable fittings 5, 6 as shown. The main chamber l is surrounded by anoven 1 which is adapted to be heated by a series of gas burners 8, 9connected to corresponding manifolds H], H leading to a source ofsuitable burner gas. Preferably the oven is surrounded with a. casing 12of asbestos or other heat insulating material. The oven and itsassociated parts are supported on suitable standards 13, while the ductsare supported on standards l4, l5, l5 and I1. Preferably the egress duct3 is surrounded with any well known form of cooling unit 18 such forexample as a series of cooling coils having a water inlet 19 and outlet20.

The duct 2 is provided intermediate its ends with an offset portion 2|the vertical end of which is provided with a window 22 of mica, glass orother similar refractory transparent material, this window being inhorizontal alignment with the main chamber I so that the parts that arebeing subjected to heat treatment therein may be viewed from theexterior. As a safety precaution the top wall of the portion 2| may beclosed by a relatively thin sheet 23 of metal such as aluminum, so thatin the event an explosive mixture should reach the section 2| this sheetwill be broken to relieve the pressure within the furnace. It will beunderstood of course that any other well known form of safety valve orthe like may be used in place of, or supplementary to the member 23.

In accordance with the invention. the hydrogen gas is admitted to themain chamber I, at the top thereof through the inlet pipes 24, 25 itbeing understood that any well known mechanism may be inserted in thehydrogen supply line to limit the pressure of the hydrogen admitted tothe furnace. Preferably also, the furnace is provided with one or more.pyrometers (not shown) for the p rpose of limiting the temperature ofthe furnace to a predetermined maximum. For the purpose of conveying thearticles 26 to be heat treated, through the furnace, there is providedan endless ggnvevqgpe lt ipg eiergply f foraminous wire mesh, this beltbeing provided wi h'EuitabIe pulleys 21, 28 driven by motor 29 at therequired rate of speed. If desired the articles to be treated may be fedinto a hopper 29a from which they may be automatically discharged on tothe moving conveyor belt by any well known mechanism. In order to guidethe conveyor bolt through the main chamber and to maintain it in spacedrelation to the bottom of the said chamber suitable water-cooled rollerbearings 30, 3| may be provided adjacent the entrance and exit openingsto the main chamber, and if desired a vertical adjustable roller 32 maybe provided to regulate the tension on the conveyor belt. After thearticles 26 emerge from the furnace they may be removed from theconveyor belt by any well known means, for example by blowing airthrough or across the belt.

As will be seen from the drawing, the hydrogen is fed into the furnaceat a point which is very much higher than the ingress and egress ends ofthe ducts 2, 3 and I have found that by properly designing theinclination and length of the ducts, the difference in level between themain chamber and the ends of the ducts is sufficient to prevent the airmixing with the hydrogen at an explosive temperature or in sufficientquantitles to form an explosive mixture. This is probably due to thefact that the hydrogen being many times lighter than air, remainstrapped within the main chamber 1 and to a certain extent within theducts 2, 3. I have also found that by making the ducts the proper lengththere is suflicient resistance to the passage of air upwardly throughthe ducts to prevent the formation of an explosive mixture within thefurnace. Preferably therefore the ducts should be of sufiicient lengththat the ingress or egress ends are removed from the main chamber sothat they are at all times below the temperature necessary to cause anexplosion, even if a small quantity of air should enter the ducts. Ifdesired the ends of the ducts may be provided with flexible curtains 33which do not disturb the articles in passing but which neverthelessprevent sudden drafts from forcing air into the furnace. Preferably alsothe hydrogen is fed into the chamber l in smooth streamlike fashion soas to agitate the contents of the chamber to the least possible extent.

In one furnace that has been constructed an found to work satisfactorilywithout any danger of explosion the chamber l was approximately 40 sq.ins. cross section and 40 ins. in length. The ducts 2 and 3 wereapproximately 108 ins. in length and the ends were disposedapproximately 16 ins. below the chamber I. The gas burners 8, 9 wereadjusted to maintain the temperature within the chamber at approximately1700 degrees Fahrenheit, the hydrogen atmosphere being at approximately15 ins. H2. In such a furnace when the parts to be treated were ordinarymetal parts such as the nickel or iron electrodes of a radio tube, theconveyor belt was run at a speed of from 6 ins. to ins. per minute.Because of the small heat content of the belt the speed of heattreatment may be increased and if the parts to be treated are disposedin a single layer on the conveyor, they are treated substantiallyuniformly over their entire surface and at a uniform temperature.

Various changes and modifications may be made in the particularembodiment described. without departing from the spirit and scope of theinvention.

What is claimed is:

1. In a furnace of the character described the combination of a mainheating chamber, an oven for heating said chamber, means forsupplyingsaid chamber with a filling of hydrogen, an inlet duct for saidchamber, an outlet duct for said chamber, a movable conveyor passingthrough said chamber and said ducts, the ends of said ducts being opento the air and situated beneath the level of said chamber, said ductsbeing proportioned in length with respect to the main heating chamber toprevent the air adjacent the open ends of the ducts from forming anexplosive mixture with the hydrogen therein and a flexible curtaindisposed over the open end of each duct to prevent the formation ofsudden drafts within the ducts.

2. A furnace according to claim 1 in which from said chamber, an ovenfor heating only the said chamber, a gogling coil surrounding theoutletvduct; both of said ducts being open to the air at their endsonly, a foraminous conveyor belt arranged to pass through said chamberand said ducts, and a pair of hydrogen supply pipes adjacent the topends of the main chamber, the ducts being of sufiicient length and beinginclined to the main chamber as to prevent the formation of an explosivemix within the furnace, and a flexible draft-preventing curtain over theend of each duct.

5. A furnace for heat treating articles in a gas which forms anexplosive mix when mixed with air at an elevated temperature, comprisinga main heating chamber, a pair of inclined ducts leading to and fromsaid chamber, means to supply the gas to said chamber at the upper endsof said ducts, a conveyor for conveying the articles through saidchamber, said ducts having their inlet and outlet ends unsealed wherebythe articles can enter and leave the furnace without being wetted, saidducts being of such length and inclination that the temperature adjacentthe open ends is below that necessary to form an explosive mix, and adraft-preventing flexible curtain covering the open end of each duct.

6. A furnace for heat treating articles in hydrogen without wetting thearticles either at their ingress to or egress from the furnace,comprising a main heating chamber, a pair of inclined ducts leading toand from said chamber, means to feed hydrogen into said chamber at theupper ends of said ducts, said duct-s having their ends open to the air,a conveyor belt passing through said ducts and chamber, said ducts beingsufliciently inclined and being suificiently long so that thetemperature adjacent the duct ends is below the

